1. Field of the Invention
This invention concerns improvements in or relating to thermostatic devices, and has special application to thermoscopic units such as are used in thermostatic devices, for instance fluid mixing valves for ablutionary appliances.
2. Description of the Prior Art
Thermostatic devices are known in which a thermoscopic unit comprises a volume of a thermally responsive material of which the change of volume is used to operate an actuator, for example to operate an actuator of a fluid mixing valve to maintain the fluid output of the valve at a predetermined substantially constant temperature.
It is already known to provide a bellows unit in which the bellows form a closed chamber inside of which the thermally responsive material is contained as a mass to which thermal changes are transmitted by heat transfer through the contact of fluid with the exposed external surface of the bellows unit.
Heat transfer to a mass of material, particularly waxes is slow and often non-uniform, and for this reason some thermoscopic units rely on vaporisation of the material, for example the use of alcohols is known. However, this invention does not intend to be applied to such materials where there is vaporisation and condensation of the thermally responsive material.